In this acoustic experiment, two Y-shaped glass tubes are connected by two flexible tubes of different lengths. Hold a struck tuning fork at the end of one tube and the waves flow down the tube to the Y where the tubes divide. However, this apparatus makes the waves in one fork of the Y travel half a wavelength farther than the waves in the other fork. When the waves meet at the other end, they’re in opposite phase to each other, so they cancel each other out. This results in no sound at all. Disconnect one of the flexible tubes and the sound reappears. Can be used at 256 Hz or 512 Hz by adjusting the length of the longer rubber tube. Requires a 256 Hz or 512 Hz tuning fork.